This is very interesting, thanks for sharing the pics, clips, and information
@fcmf Just out of curiosity I had a bit of a rummage around on some other sites and there seemed to be so many comments that made sense. From the comments regarding any genetically deformed fish, or fish that may develop deformities through illness of injury usually not surviving in the wild, to problems with inbreeding due to commercial farming of fish. From general old age, again wild verses tank environments, to water parameters. From fish TB (or not), to shock.
The comments and articles that I came across also seemed to cover a variety of fish, various tank inhabitants through to pond koi. I also came across a lot of comments about fish TB being contagious (generally terminal) so unlikely if only some fish effected.
Again, I have to state these were comments I came across during a rummage, not scientific articles from trusted sources found whilst researching. Perhaps it's worth sending the info & pics to the "readers questions" section of PFK to see if they picked up on this topic.
Although I would like to highlight my favourite comment, which was one regarding fish TB, and one chap said he didn't know how closely fish TB was related to human TB, but wasn't aware of fish diseases being passed to humans, with the exception of MTS (multi-tank syndrome).